TempoLife › Features › Muscle and body-part reference › iliopsoas
Iliopsoas
The strongest hip flexor, and the only muscle connecting the lumbar spine directly to the leg.
Latin name: Musculus iliopsoas. In plain English, the deep hip flexor that runs from the lower spine to the thigh. It is filed here under hip and buttock.
Reference information, not a diagnosis. Where a symptom is described below, it is there so you can describe your own more precisely to a clinician — not so you can name what you have.
Where it is
Psoas major runs down inside the abdomen along the front of the lumbar spine, crosses the brim of the pelvis, and joins iliacus, which lines the inner surface of the pelvic bowl. Together they pass under the inguinal ligament, in front of the hip joint, to a single tendon on the lesser trochanter — a bump on the inner side of the top of the thigh bone.
Because it starts on the spine and ends on the leg, iliopsoas is the only muscle that spans that gap. It also lies deep: it is behind the abdominal contents, and pressing on it through the belly, as some manual techniques suggest, means pressing through structures that would rather be left alone.
| Feature | Detail |
|---|---|
| Origin | Psoas major from the bodies, discs and transverse processes of T12 to L5; iliacus from the iliac fossa on the inner surface of the pelvis |
| Insertion | Lesser trochanter of the femur, by a common tendon |
| Nerve | Psoas major by the anterior rami of L1-L3 directly; iliacus by the femoral nerve (L2-L4) |
| Main actions | Flexion of the hip; with the leg fixed, flexion of the trunk toward the thigh, and influence on the lumbar spine |
What it does
It is the primary hip flexor and by some distance the strongest one — every step, every stair, every knee lift and every sit-up with straight legs uses it. When the femur is fixed and the trunk moves instead, it flexes the trunk, which is why it works so hard in a full sit-up and why sit-ups feel different from a curl-up.
Its effect on the lumbar spine is more debated than most people realise. It clearly crosses the lumbar segments and can compress and stabilise them; whether a tight psoas pulls the spine into an arch as commonly claimed is far less certain. Sitting for hours holds the muscle short, but "tight hip flexors cause back pain" is an assumption, not an established chain of cause and effect.
Exercises that load it
| Exercise | Category | Muscles the exercise library lists |
|---|---|---|
| Sit-ups | Core | Abdominals, hip flexors |
| Mountain climbers | Conditioning | Core, hip flexors, shoulders |
| Tempo running (12 km/h) | Cardio | Legs, heart, lungs |
| Lunges | Strength | Quads, glutes, hamstrings, balance |
| Stair climbing | Cardio | Quads, glutes, calves, heart |
Anything that lifts the knee against resistance loads it: hanging knee raises, high-knee running, hill work, stairs. Sprinting loads it hard and quickly, which is why hip flexor strains show up in sprint sports. Because it works at the end of hip extension too, controlled work in a lengthened position — for instance a split squat with the back hip fully open — is worth more than repetitions in the middle of the range.
How it is lengthened
A half-kneeling lunge with the back hip extended, the pelvis tucked underneath, and the ribs kept down. Without the pelvic tuck, most people simply arch the lower back and feel nothing useful. Adding a small side bend away from the back leg takes it further. Thirty seconds a side, done regularly, does more than one long session.
When it goes wrong
| Problem | What it typically feels like | Usual setting |
|---|---|---|
| Hip flexor strain | A pull at the front of the hip or in the groin when lifting the knee or sprinting | Sprinting, kicking, or a sudden increase in high-knee work |
| Iliopsoas tendinopathy or snapping hip | A deep front-of-hip ache with an audible or palpable snap as the tendon moves over bone | Repeated hip flexion under load — dance, running, cycling |
| Iliopsoas bursitis | A deep groin ache, worse on extending the hip or after long sitting | Overuse, or irritation of the bursa between tendon and joint |
Groin pain in a runner that fails to settle can be a bone stress injury of the femoral neck, which is a serious diagnosis. Groin pain with fever, or with an inability to weight-bear, needs urgent assessment.
Nothing on this page is a treatment plan. If a problem is limiting what you do, is not improving, or is getting worse, the right next step is an assessment by a doctor or a physiotherapist who can examine you.
Sources: descriptive anatomy from Gray's Anatomy of the Human Body, 20th US edition (1918), which is in the public domain; Latin names follow Terminologia Anatomica, published by the Federative International Programme for Anatomical Terminology. Nerve root levels are the conventional ranges taught from those sources and vary between individuals and between textbooks. Exercise cross-links use the TempoLife exercise library. Checked 2026-09-06.
Frequently asked questions
Does sitting shorten the psoas?
Sitting holds the hip flexed, so the muscle spends long periods short. Whether that produces a lasting change in muscle length in most people is less clear than the popular story suggests, and the effects of long sitting on the body are broader than any one muscle.
Should I have my psoas released by massage?
The muscle lies deep behind the abdominal organs, so pressing on it from the front means pressing through them. Effective work on the hip flexors is usually done through movement and loading rather than through deep abdominal pressure.
Why do sit-ups hurt my lower back?
A full sit-up with the feet held recruits the hip flexors strongly and they pull on the lumbar spine. Curl-ups with a smaller range, or dead bugs, load the abdominal wall with less pull on the back.
Nearby in this reference
Gluteus maximus
The main buttock muscle
Gluteus medius
The side-hip muscle that keeps the pelvis level
Piriformis
The deep rotator behind the hip, next to the sciatic nerve
Tensor fasciae latae
The small front-of-hip muscle that tightens the IT band
Hip adductors
The inner thigh muscles
Deltoid
The cap of the shoulder
All 34 body parts · Exercise library · Body map
Training is easier to judge when it is written down
TempoLife logs workouts, steps and sleep together, so a week of training and a week of recovery can be read side by side.